Electrolytic process for preparing(2.2)-paracyclophane

ABSTRACT

(2.2)-Paracyclophane is prepared by electrochemically reducing a sulfonium salt having the formula   WHEREIN R1 and R2 are alkyl or hydroxy-substituted alkyl radicals of one to 10 carbon atoms and A is an electrolytically acceptable anion. The process is conducted at low current densities.

United States Patent [721 Inventors [21 Appl. No. [22] Filed [45 Patented [73] Assignee [54] ELECTROLYTIC PROCESS FOR PREPARING[2.2]-

PARACYCLOPHANE 7 Claims, N0 Drawings [52] US. Cl 204/59, 204/7 2 [51] lnt.Cl 301k 3/00 [50] Field of Search 204/59, 72

[56] References Cited UNITED STATES PATENTS 3,399,124 8/1968 Gilch 204/72 3,480,525 11/1969 Wesslinget al. 3,417,003 12/1968 Rossetal Primary Examiner-John H. Mack Assistant Examiner-Neil A. Kaplan AttorneysGriswold & Burdick and C. E. Rehberg ABSTRACT: [2.21-Paracyclophane is prepared by electrochemically reducing a sulfonium salt having the formula:

wherein R, and R are alkyl or hydroxy-substituted alkyl radicals of one to 10 carbon atoms and A is an electrolytically acceptable anion. The process is conducted at low current densities.

ELECTROLYTIC PROCESS FOR PREPARING[2.2]-

PARACYCLOPIIANE BACKGROUND OF THE INVENTION The preparation of [2.2]-paracyclophane by the electrochemical reduction of a,a'-dibromo-p-xylene was described by F. H. Covitz, J. Am. Chem. Soc., 89, No. 21,5403 (1967). Covitz exhaustively electrolyzed at -1.5 volts a dilute solution of a,a'-dibromo-p-xylene in dimethylformal wherein X is a halogen or lower alkyl group n is an integer of from 0 to 4 R is a lower alkyl or hydroxyalkyl group, and A is an electrolytically acceptable anion (typically an anion of a strong acid), in solution with an electrolysis solvent to an electrical potential sufficient to reduce the sulfonium salt. The concentration of the sulfonium salt in the electrolysis solvent was generally from 0.01 to 4 moles/liter, and a cathode voltage of -l.0 volts (versus a saturated calomel electrode) at about 120 milliamperes (ma.) per 50 cmFcathode area was preferred in aqueous media. The above process was conducted in an electrolysis system comprising an anode, a cathode, an electrolysis solvent and a means for applying and maintaining an electrical potential between said anode and cathode.

SUMMARY OF THE INVENTION It has now been discovered that [2.21-paracyclophane, i.e.,

in a dilute solution in an electrolysis solvent to an electrical potential sufficient to reduce the sulfonium salt at an amperage of from about to about 60 milliamperes per 50 cm. of cathode surface; in II above, R, and R are a lower alkyl or hydroxyalkyl group of from 1 to about 10 carbon atoms and preferably one to about four carbon atoms, and A is an electrolytically acceptable anion, such as the anion of a strong acid or an organic anion, such as a tosylate anion. [2.2 ]-Paracyclophane is a known compound having demonstrated utility, such as an intermediate in the preparation of poly(pxylylene).

The subject process substantially differs from Covitz by the reactants used. The sulfonium salts used herein are much more versatile and easily reduced than the benzyl halides used by Covitz, particularly in aqueous media. The subject process also differs from the process defined in our copending applica tion, Ser. No. 647,895, by the process parameters placed on the current density and/or concentration of the sulfonium salt in the electrolysis solvent and temperature.

ELECTRICAL POTENTIALS The cathode potential (reducing potential) may vary depending upon the sulfonium salt and other process variables but must be sufficient to reduce the sulfonium salt. Due to their relative case of reduction, cathode potentials of from about 0.5 to about -l.0 volts (versus a standard saturated calomel electrode (SCE)) is generally operable, although in some instances slightly higher or lower voltages may be used. The rate of reduction increases as the voltage becomes more negative; however, the amount of byproducts also increase in a like manner.

Seemingly more important than the cathode potential is the current density, as expressed in milliamperes (ma.) per 50 cm? of cathode surface. A suitable current density is from about 5 to about ma./50 cm. At a current density higher than about 60 ma./50 cm. the process is operably but increasing amounts of byproduct are formed, and at a current density below about 5 ma./50 cm, the reaction rate is too slow to be practical.

ELECTROLYTE CONCENTRATION The concentration of the sulfonium salt in the electrolysis solvent may suitably be from about 10" to about 10" moles/liter. However, the critical factor controlling the yield of [2.2]-paracylophane is the current density. If cathode potentials are selected from the negative end of their range, then concentrations at the lower end of the range are preferred in order to keep the current densities low; however, any combination of the sulfonium salt concentration and the cathode potential that produces a current density within the defined limits may be used.

The electrolysis solution may advantageously contain a supporting electrolyte. Compounds useful for this purpose form a known class which includes salts of strong acids such as KCl, NaBr, Na=SO Na PO and the like, the ammonium salts, such as tetraethylammonium chloride, ammonium iodide, and the like. When used, the supporting electrolyte is generally included in the electrolysis solution in an amount from about 0.1 to about 4 moles/liter. Ideally, the anion of the supporting electrolyte is the same as A in II above.

SULFONIUM REACT ANTS Suitable sulfonium salts in the subject process are represented by II above. Examples of suitable such salts include those of Formula II wherein.

and other like compounds. Their methods of preparation are known in the art. The anion is advantageously chosen to increase the solubility of the sulfonium salt in the electrolysis solvent; e.g. if the anion is a halide, the salt is generally quite soluble in water, if the anion is an organic radical, such as tosylate, the sulfonium salt will generally be soluble in a polar organic solvent, such as dimethylformamide.

SOLVENTS Any compound which dissolves or substantially disperses the sulfonium salt and is otherwise inert in the process is a suitable solvent. Suitable solvents include water and polar organic solvents, such as dimethylforrnamide, dioxane, hexamethyl phosphoramide, acetonitrile, propionitrile, methanol, ethanol, and the like. The preferred solvent is hexametyl phosphoramide. Mixtures of organic solvents, and mixtures of water and organic solvents are likewise suitable.

CATHODES Mercury is the preferred cathode since it is liquid and can be easily stirred to give a continued fresh cathode surface. The mercury cathode is generally either a stirred pool in the electrolysis cell or a dropping mercury cathode; a stirred pool is currently preferred. In either instance, the electrolysis solution (catholyte) is preferably stirred.

CELL PARAMETERS The essential components of the cell are (1) an anode, 2) a cathode, and (3) a means for applying and maintaining an electrical potential between the anode and cathode. The cathode has been discussed above; the anode may be substantially any electroconductive materials, although graphite or platinum are generally used; the means for applying the potential is suitably (a) a source of direct current, wherein the cathode potentials varies to a more negative value as the concentration of sulfonium salt decreases, or (b) a variable source of power which is adjusted to maintain the cathode potential and/or the current flow at a predetermined level. The latter instance is preferred and is referred to as controlled-potential electrolysis. See L. Meites, Techniques of Organic Chemistry, A. Weissberger- Editor, Vol. 1, 3rd ed., p. 3281, Interscience, NY. (1959), for a discussion of controlled-potential electrolysis and a cell description.

SPECIFIC EMBODIMENTS The following example further illustrates the invention:

A three-compartment cell of the type described by Meites was employed. The cathode compartment and contents were maintained in "an inert gas atmosphere, such as argon or nitrogen, during the electrolysis. A direct current was supplied to the cell with a variable potential difference between the anode (graphite) and cathode (mercury) in order to maintain a constant cathode potential. The cathode was a stirred mercury pool having 50 cm. surface area. Reaction temperature 60 C.

a,a'-bis(dimethylsulfonium tosylate)-p-xylylene (4g.) was dissolved in 200 ml. of 0.75 tetraethylammonium tosylate in hexamethylphosphoramide and added to the cathode compartment. The cathode potential was set at 0.68 volts a standard saturated calomel electrode. The amperage ranged from an initial value of [6 ma. to 1 ma. over 28 hours. The solid product formed at the cathode was removed by filtration, extracted with p-xylene C.) for 2 hours and filtered from the hot xylene. The residual solvent was removed by a nitrogen stream and the residue (0.5 C.) analyzed by mass spectroscopy. The yield of [2.21-paracyclophane was 8 percent based on the initial weight of the sulfonium salt. [2.2]- paracyclophane was also produced in other similar experiments except for the solvent which was water, dimethylformamide, or methanol. Similar results are obtained by using other sulfonium salts.

We claim:

1. An electrolytic process for preparing [2.2]-paracyclophane comprising electrochemically reducing a sulfonium salt having a formula wherein R, and R are alkyl or hydroxy-substituted alkyl radicals of one to l Ocarbon atoms and A9 is an electrolytically acceptable anion; said reduction being conducted in an electrolytic system comprising an anode, a cathode, an electrolysis solvent and a means for applying and maintaining an electrical potential between said anode and cathode and recovering said [2.2] -paracyclophane.

2. The process defined in claim 1 wherein the current flow between said anode and cathode is a value of from 5 to 60 milliamperes per 50 cm. of surface area and wherein the cathode potential is from 0.5 to 1.0 volts.

3. The process defined in claim 1 wherein the concentration of said salt in said electrolysis solvent is from 10 to 10 moles/liter.

4. The process defined in claim 3 wherein the current flow between said anode and cathode is a value from 5 to 60 milliamperes per 50 cm. of surface area and the cathode potential is from 0.5 to 1.0 volts.

5. The process defined in claim 4 wherein said electrolysis solvent is water. hexamethyl phosphoramide, dimethylformamide or lower alkanol of one to four carbon atoms.

6. The process defined in claim 5 wherein said cathode is mercury.

7. The process defined in claim 6 wherein said cathode is a stirred mercury pool and said solvent is hexamethyl phosphoramide and A is a tosylate anion.

P040250 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,616,31 Dated 26 October 1971 William J. Settineri and Ritchie A. Wessli no It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In column 1, line 28, delete "A" and insert A in line 29 delete 'TE' In column 2, line 17, delete "operably" and insert operable in line 2 4 delete lOT and insert l0 and delete "lO and insert 10' in Table 1 between lines 50 and 65 change the third column to Br tosylate' Cl- N03 SO Cl- In column 3, line 50, insert 1. between "volts" and In column b, line 36, delete "10 and insert 10 and delete "10 and insert l0 Signed and sealed this 16th day of Mm; 197?.

[CD11 .RII PLFLETGHER ,JR ROBERT GOTTSCHALK Ami/rating Officer Commissioner of Patents 

2. The process defined in claim 1 wherein the current flow between said anode and cathode is a value of from 5 to 60 milliamperes per 50 cm.2 of surface area and wherein the cathode potential is from -0.5 to -1.0 volts.
 3. The process defined in claim 1 wherein the concentration of said salt in said electrolysis solvent is from 10 4 to 10 2 moles/liter.
 4. The process defined in claim 3 wherein the current flow between said anode and cathode is a value from 5 to 60 milliamperes per 50 cm.2 of surface area and the cathode potential is from -0.5 to -1.0 volts.
 5. The process defined in claim 4 wherein said electrolysis solvent is water, hexamethyl phosphoramide, dimethylformamide or lower alkanol of one to four carbon atoms.
 6. The process defined in claim 5 wherein said cathode is mercury.
 7. The process defined in claim 6 wherein said cathode is a stirred mercury pool and said solvent is hexamethyl phosphoramide and A is a tosylate anion. 